The invention relates generally to an exchanger tube for a heat exchanger. More particularly, the invention relates to an exchanger tube of the type having a structured inner surface formed from ribs running at an angle with respect to the longitudinal tube axis and having inclined flanks and channels that are limited laterally by the ribs and troughs. These channels extend transversely through the ribs and also have inclined flanks, which extend at an angle with respect to the longitudinal tube axis.
An exchanger tube of this general type is described in EP 0 692 694 A2 (the corresponding U.S. Pat. No. 5,458,191 is incorporated herein by reference). In this case, both the ribs and the channels that are limited laterally by the ribs each have a trapezoidal cross section. The flanks of the ribs are planar, the transitions from the flanks to the channel beds are sharp-edged. Sharp-edged transitions are also present between the flanks and the level top sides of the ribs. The rib cross-sectional volume is dimensioned to be approximately one-half that of the channels. The parallel ribs extend at a 90.degree. angle with respect to the longitudinal tube axis. All of the ribs have the same radial height.
The troughs extending transversely through the ribs likewise run at a 90.degree. angle with respect to the longitudinal tube axis. The trough flanks are arched convexly. The transitions from the flanks to the level beds of the troughs, and to the level top sides of the rib regions between two adjacent troughs of a rib, are sharp-edged. The depth of the troughs is dimensioned to be less than the radial extension of the ribs. All of the troughs are of identical depth. In producing the troughs, the material formed from the ribs is shaped into the channels on the end face of the troughs.
The preferred method of producing the known exchanger tube is first to perform a rolling process to create the structure on one side of a metal band that will later be the inside surface, then shape the metal band into a slit tube with the surface structure on the inside, and then weld the slit edges together.
Because of the flat top sides and the level flanks of the ribs, in practical use the exchanger tube can be subject to the formation of condensate films that are difficult to remove and that retard condensation. Hence, blocking layers having thermally-insulating properties can form, leaving only a few edges available for developing steam bubbles for evaporation.
There remains a need for a heat exchanger tube having an inside surface structure with which a clearly more intensive channel flow-through can be assured, and which combines the advantages of uniformly good evaporation or condensation performance and a reduced rib weight.